Re: [RFC PATCH] crypto: crc32c-pclmul - Use pmovzxdq to shrink K_table

Dave Jones
2014-05-30T01:17:44Z

On Thu, May 29, 2014 at 06:07:16PM -0700, Tim Chen wrote:
> On Thu, 2014-05-29 at 19:54 -0400, George Spelvin wrote:
> > Sorry for the delay; my Ivy Bridge test machine isn't in my
> > office and getting to the console to tweak the BIOS is a
> > bit of a bother.
> >
> > Anyway, i7-4930K, turbo boost & hyperthreading disabled,
> > $ cat /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor
> > performance
> > performance
> > performance
> > performance
> > performance
> > performance
> >
> > Oddly, though, CPU speed still seems to be fluctuating:
> > $ grep MHz /proc/cpuinfo
> > cpu MHz : 1255.875
> > cpu MHz : 3168.375
> > cpu MHz : 3062.125
> > cpu MHz : 1468.375
> > cpu MHz : 1309.000
> > cpu MHz : 2212.125
> > $ grep MHz /proc/cpuinfo
> > cpu MHz : 1255.875
> > cpu MHz : 2690.250
> > cpu MHz : 1255.875
> > cpu MHz : 2530.875
> > cpu MHz : 2212.125
> > cpu MHz : 1521.500
>
> This is odd. On my Ivy Bridge system the CPU speed from /proc/cpuinfo
> is at max freq once I set the performance governor.
> The numbers above almost look like
> the cpu frequency is fluctuating and an average is taken.
> What version of the kernel are you running? Is
> CONFIG_CPU_FREQ_GOV_PERFORMANCE compiled in?
>
> Does /sys/devices/system/cpu/cpu?/cpufreq/scaling_cur_freq
> also changes?
>
> Can you check what are the available governors in your system
> and available frequencies?
>
> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
>
> If userspace governor is available, you can try set the governor
> to userspace, then pin frequency to 3400 MHz (assuming that's your
> max) with command like:

intel_pstate overrides any governor choice you make through sysfs.

Dave